EP2194191A1

EP2194191A1 - A vibratory mechanism for a pile driver and a pile driver

Info

Publication number: EP2194191A1
Application number: EP08170711A
Authority: EP
Inventors: Jasper Stefan Winkes
Original assignee: Fistuca BV
Current assignee: Fistuca BV
Priority date: 2008-12-04
Filing date: 2008-12-04
Publication date: 2010-06-09
Also published as: US20110240323A1; EP2370642A1; WO2010063764A1

Abstract

A vibratory mechanism (1) for a pile driver comprises a static part (2) and a dynamic part (3). The dynamic part (3) is movable with respect to the static part (2). The static part (2) is provided with a drivable crankshaft (6) and the dynamic part (3) comprises a housing (13) and a vibration member (7). The vibration member (7) is drivably coupled to the crankshaft. (6) through a connecting rod (8) and linearly movable with respect to the housing (13) in a direction of vibration. The housing (13) is resiliently coupled to the vibration member (7).

Description

The invention relates to a vibratory mechanism for a pile driver comprising a static part and a dynamic part being movable with respect to the static part.
Such a vibratory mechanism is known from US 5,088,565 . The static part of the prior art mechanism is attached to a cable of a crane and the dynamic part comprises jaws for clamping a pile to be driven, into the ground or to be extracted out of the ground. The dynamic part is provided with a pair of eccentrically rotatable weights which can be rotatably driven by a hydraulic motor. The weights rotate in opposite directions with respect to each other resulting in a vertical vibration of the dynamic part. A disadvantage of the known mechanism is that bearings of the rotatable weights are heavily loaded resulting in relatively high operational costs due to maintenance and replacement of the bearings.
The object of the invention is to provide a simple and robust vibratory mechanism.
This object is achieved by the mechanism according to the invention which is characterized in that the static part is provided with a drivable crankshaft and the dynamic part comprises a housing and a vibration member being drivably coupled to the crankshaft through a connecting rod and linearly movable with respect to the housing in a direction of vibration, wherein said housing is resiliently coupled to the vibration member.
Upon driving the crankshaft the vibration member will vibrate linearly with respect to the housing of the dynamic part. Due to the resilient coupling between the vibration member and the housing, the housing of the dynamic part will vibrate as well. In case the vibratory mechanism is applied in a pile driver the housing of the dynamic part may be provided with clamping means for clamping a pile. The mechanism according to the invention provides the opportunity to select the rotation speed of the crankshaft, the weights of the vibration member and the housing and the degree of resiliency between the vibration member and the housing such that the dynamic part vibrates at a certain frequency, whereas transfer of inertia forces in the mechanism via the crankshaft to the remainder of the static part is minimized. In fact the reciprocating forces of the first order, affected by the vibration member weight, can be used to balance the vibrational forces of the housing of the dynamic part on the crankshaft under certain conditions. This means that forces on crankshaft bearings in the static part are minimized, hence reducing wear and operational costs. It is noted that the term "reciprocating forces of the first order" is typically used in case of balancing reciprocating piston-crank-connecting rod mechanisms, such as present in internal combustion engines, in order to indicate inertial forces of the piston acting in the direction of piston movement and occurring at the frequency of rotation of the crank.
A further advantage of the crank-connecting rod mechanism is that it can be built in a compact way compared to a conventional dynamic part comprising oppositely rotating weights, since in the latter case at least two rotatable weights must be located next to each other as seen in horizontal direction so as to achieve a vertical vibration.
Moreover, due to the resilient coupling between the housing and the vibration member sudden peak forces on the housing are not directly transferred to the vibration member and the static part. Such a sudden peak force may typically happen in a pile driver if a pile is fixed to the housing to be driven into the ground and the pile touches a rigid layer or a stone or the like. The resulting so-called rebound effect is smoothly transferred to the static part by the mechanism according to the invention.
The housing may be resiliently coupled to the vibration member via a fluid spring. An advantage of a fluid spring is that its spring characteristics can be influenced by modifying its fluid properties.
In a practical embodiment the vibration member is a piston and the housing comprises a cylinder within which the piston is slidable, and the fluid spring is formed by a fluid chamber being present between the piston and the cylinder. When the piston is movable in the cylinder and a fluid such as air or an alternative gas is present in the fluid chamber, the fluid chamber functions as a fluid spring.
In a preferred embodiment the fluid spring is formed by two fluid chambers located at opposite sides of the piston. This provides more flexibility in influencing the spring characteristics of the resiliency between the piston and the cylinder.
The fluid chambers may be allowed to communicate with each other through a controllable valve. When opening the valve and moving the piston within the cylinder the fluid will flow from the fluid chamber of which the volume reduces to the fluid chamber of which the volume increases. If the valve is open such that no compression/expansion occurs in the fluid chambers the spring characteristics created by the fluid chambers are negligible. This may be desired under certain conditions, for example in case of a pile driver which is starting-up. In that case the housing should not be driven before the piston vibration has reached a certain frequency. When the valve is open the piston may vibrate within the cylinder without driving the housing of the dynamic part. In practice, when the vibratory mechanism is applied in a pile driver the valve may be closed at a piston frequency exceeding for example 1200 rpm, such that the starting-up period during which the frequency of the housing of the dynamic part is relatively low, is short.
It is also conceivable that the fluid chambers communicate with the ambient air through a controllable valve during the starting-up period.
In an alternative embodiment the mechanism comprises at least two vibration members, wherein the mechanism is adapted such that under operating conditions the vibration members can be driven in opposite directions, for example in counter phase. This allows the opportunity to increase the vibration frequency of the vibration members to a relatively high level, for example the operational frequency in case of a pile driver, whereas the vibration of the housing in the direction of vibration remains negligible, because the forces of the oppositely moving vibration members on the housing via the resiliency can be balanced.
Preferably, the characteristics of the resiliency between the housing and the vibration members can be varied. Due to this feature the resiliency can be adjusted such that the counter force, of the resiliency on the vibration members at least partly reduce the inertia forces of the vibration members on the static part during the increase of the vibration frequency of the vibration members whereas the vibration of the housing remains negligible. When reaching the operational speed, and vibration of the housing is desired, the mechanism can be set such that the vibration members move synchronously in the same direction. In practice, during increase of the frequency the resiliency will be adjusted to a stiffer level.
In case the vibrating members are pistons moving oppositely in corresponding cylinders and the resiliency is formed by the fluid chambers located at opposite sides of each of the pistons, the fluid pressure in the fluid chambers can be increased during the period of increasing the frequency of the reciprocating speed of the pistons in order to reduce the reciprocating inertial forces of the pistons on the static part.
In an embodiment which comprises at least two pistons and two corresponding cylinders the fluid chamber of one cylinder can communicate with the fluid chamber of the other cylinder such that under operating conditions a decreasing fluid chamber volume in one cylinder can communicate with an increasing fluid chamber volume in the other cylinder. During starting-up of, for example, a pile driver the fluid chambers can be connected to each other in fluid communication which means that the piston in one cylinder pushes the fluid from the fluid chamber in that cylinder to the fluid chamber of the other cylinder, whereas the piston of the other cylinder synchronously sucks the fluid from the one cylinder. During such a starting-up period the pistons vibrate within the cylinders without driving the housing of the dynamic part.
In case the pistons can be driven in counter phase two cylinders may be disposed parallel to each other and the fluid chambers at the same side of the pistons can be connected to each other. During the starting-up period the pistons can be driven in counter phase such that the volumes of the mutually connected fluid chambers at the same side of the pistons also vary in counter phase. As a consequence, the sum of the volumes of the connected fluid chambers substantially remains the same. Of course, the fluid communication can be effected by a controllable valve or the like.
Alternatively, the mechanism may comprise adjusting means for adjusting the stroke of the vibration member with respect to the eccentricity of the crankshaft in order to minimize the amplitude of the vibration member during a starting-up period.
In a particular embodiment the fluid spring can communicate with compressing means for increasing or decreasing the pressure of the fluid in the fluid spring. This feature provides the opportunity to influence the amplitude of the housing, for example. A variable pressure, depending on the operation frequency is also conceivable.
The housing of the dynamic part and the static part may be connected to each other via a spring and/or a damper so as to create a coupling between the static part and the dynamic part in addition to the coupling via the connecting rod, and to reduce any transfer of vibrations from the dynamic part to the static part.
In a particular embodiment a first part of the connecting rod is guided by a crosshead guide in the static part or in the dynamic part and a second part thereof being fixed to the vibration member is movable along its longitudinal centre line only. This means that the second part has a one-dimensional motion in the direction of vibration of the vibration member.
In a preferred embodiment the vibration speed of the vibration member, the weight of the housing and the characteristics of the resiliency between the housing and the vibration member are selected such that the vibration member and the housing substantially vibrate in counter phase under operating conditions, and the weight of the vibration member is selected such that its inertia force of the first order substantially balances the inertia force of the housing. In practice, the weight of the vibration member and the housing may be selected first and the characteristics of the resiliency between the housing and the vibration member is then adjusted to optimize the functioning of the mechanism. For example, the characteristics of the resiliency can be influenced by the volume of the fluid chamber in case of a fluid spring.
The invention is also related to a pile driver comprising a vibratory mechanism as described hereinbefore.
The static part of the vibratory mechanism may be provided with driving means for driving the crankshaft. This is advantageous in terms of mobility compared to a mobile pile driver of which the driving means are located on the ground. This is also advantageous in terms of efficiency and reduced complexity with respect to conventional pile drivers in which hydraulic systems are used and power must be transmitted from a power supply on the ground to the static part.
Preferably, the driving means is an internal combustion engine.
The invention will be explained in more detail hereinafter with reference to drawings, which are schematic representations of embodiments of the invention.
Fig. 1 is a schematic view of an embodiment of the vibratory mechanism according to the invention.
Fig. 2 is a perspective view of an alternative embodiment of the vibratory mechanism of Fig. 1.
Fig. 3 is a similar view as Fig. 1 of an alternative embodiment on a smaller scale.
Fig. 1 shows an embodiment of the vibratory mechanism 1 according to the invention. The vibratory mechanism 1 is part of a pile driver in this example, but may be suitable for alternative technical devices.
The vibratory mechanism 1 as shown in Fig. 1 comprises a static part 2 and a dynamic part 3. The dynamic part 3 is movable with respect to the static part 2. The static part 2 is provided with a lifting eye 4. In a pile driver the lifting eye 4 suspends from a cable of a crane (not shown). The dynamic part 3 is provided with a pair of clamps 5 for clamping a pile to be driven into the ground or to be extracted out of the ground. The pair of clamps 5 may be driven mechanically, hydraulically or the like.
Under operating conditions the dynamic part 3 oscillates in vertical direction at a predetermined frequency and with a predetermined amplitude with respect to the static part 2.
Fig. 1 shows that the static part 2 is provided with a drivable crankshaft 6. The crankshaft 6 comprises two crankpins located eccentrically with respect to the centre line of the crankshaft 6.
The dynamic part 3 is provided with two pistons 7 as vibration members. Each of the pistons 7 is coupled to the crankshaft 6 through a connecting rod 8. In this case the connecting rod 8 comprises a first part 9 which is guided by a crosshead guide 10 in the static part 2, and a second part 11 which is movable along its longitudinal centre line only. The piston 7 is fixed to the second part 11. As a consequence of this configuration, a through hole in the dynamic part 3 through which the second part 11 of the connecting rod 8 moves up and down may have the shape of the cross-sectional area of the second part 11 and the dimensions of the cross-sectional area of the through hole may be slightly larger than those of the second part 11.
In the embodiment as shown in Fig. 1 the crankshaft 6 is driven by an internal combustion engine 12. Alternative driving means are conceivable, for example a hydraulic or electric motor. An advantage of applying the internal combustion engine 12 is that it can be used as stand-alone unit in the static part 2.
The dynamic part 3 further comprises a housing in the form of cylinders 13 which function as guides for guiding the pistons 7. The cylinders 13 have a fixed position with respect to the dynamic part 3. The pistons 7 are slidable within the cylinders 13. The cylinders 13 are filled with a fluid, for example air. In each of the cylinders 13 the piston 7 divides the cylinder space into two fluid chambers 14, 15 located at opposite sides of the piston 7. If the fluid chambers 14, 15 are closed spaces or nearly closed spaces, they form a fluid spring. This means that the housing of the dynamic part 3 or the cylinder 13 is resiliently coupled to the piston 7. In case the fluid is a gas, the fluid chambers 14, 15 form a gas spring.
The fluid spring characteristics can be adjusted by modifying the fluid properties in the fluid chambers 14, 15. In the embodiment of Fig. 1 the fluid chambers 14, 15 can communicate with each other through a controllable valve 16. When the valve 16 is fully opened the fluid chambers 14, 15 communicate with each other. This means that in case of a downward displacement of the piston 7 the fluid from the lower fluid chamber 15 is pressed to the upper fluid chamber 14 via the valve 16. In that case the housing of the dynamic part 3 or the cylinder 13 will not follow the displacement of the piston 7. When the valve 16 is closed and the piston 7 is displaced downwardly the fluid in the lower fluid chamber 15 will be compressed and the fluid in the upper fluid chamber 14 will be expanded. As a result the cylinder 13 will follow this displacement in downward direction. Depending on the frequency of the piston movement, the weight of the housing of the dynamic part 3 and the properties of the fluid in the fluid chambers 14, 15 the housing of the dynamic part will 3 will follow the piston movement at a certain phase shift, comparable to a conventional spring-mass system.
It appears to be advantageous to select the influencing parameters of the mechanism 1 such that the pistons 7 and the housing of the dynamic part 3 vibrate in counter phase. In this case the actual inertia force of the housing of the dynamic part 3 is directed opposite to the actual deceleration of the pistons 7. Since the inertia force is transferred to the static part 2 via the connecting rod 8 and the crankshaft 6, vibrations of the dynamic part 3 would be transferred to the static part, as well, and bearings of the crankshaft 6 would be loaded heavily. However, this effect can be minimized by selecting the weights of the pistons 7 such that inertia forces of the first order, generated by the pistons 7, balance the inertia force of the housing of the dynamic part 3. The inertia forces of the first order are directed in the direction of deceleration of the pistons 7.
The valve 16 can also be used in case of starting-up the vibratory mechanism 1. In case of driving a pile into the ground it may be desired to avoid low frequency vibrations which might occur during a starting-up period of the mechanism 1. This can be avoided by opening the valve 16 during increase of frequency of the piston 7 such that the housing of the dynamic part 3 remains in a non-vibration mode. Once a predetermined desired frequency has been reached the valve 16 is closed and the starting-up period of vibration of the housing of the dynamic part 3 up to its desired frequency is relatively short. Alternatively, an adjusting mechanism (not shown) for adjusting the piston stroke with respect to the eccentricity of the crankshaft 6 may be present.
The spring characteristics of the fluid chambers 14, 15 can be influenced by varying the pressure of the fluid. This can be achieved by applying a compressor (not shown) which increases or decreases the fluid pressure in the fluid chambers 14, 15 via a press line 17.
It is noted that it is not necessary that the fluid chambers 14, 15 can communicate with each other. It is also possible to vent the fluid chambers 14, 15 to the ambient air during the starting-up period, such that pressure build-up in the fluid chambers 14, 15 is negligible.
The vibratory mechanism 1 further comprises springs 18 to hold the static part 2 and the dynamic part 3 at a substantially constant distance with respect to each other. The spring 18 may also have damping characteristics to eliminate any residual vibrations between the static part 2 and the dynamic part 3.
Fig. 2 shows an alternative embodiment of the vibratory mechanism 1 as part of a pile driver. The reference signs of the embodiment of Fig. 2 refer to similar components as being present in the embodiment of Fig. 1. The embodiment as shown in Fig. 2 is provided with a single piston 7. This provides the opportunity to design a compact vibratory mechanism 1 as seen in a direction perpendicular to the direction of vibration of the piston 7.
Fig. 3 shows another alternative embodiment, which is provided with four pistons 7 in line. The reference signs in Fig. 3 refer to corresponding components as shown in Fig. 1. It can be seen that each piston 7 is coupled to a separate crankshaft 6a-6d. Two inner crankshafts 6b, 6c located between two outer crankshafts 6a, 6d are driven by the internal combustion engine 12 via a first transmission 19 and the outer crankshafts 6a, 6d are driven via a second transmission 20. During a starting-up period the first and second transmissions 19, 20 are controlled such that the two inner pistons 7 located in the middle of the dynamic part 3 are moving in counter phase with respect to the two outer pistons 7 located at the outer sides of the dynamic part 3, as indicated by arrows in Fig. 3. During this period the valves 16 are open. When both inner pistons 7 move upwardly and both outer pistons 7 move downwardly the fluid in the upper fluid chambers 14 of both inner cylinders 13 flow to the associating upper fluid chambers 14 of both outer cylinders 13, and the fluid in the lower fluid chambers 15 of both outer cylinders 13 flow to the associating lower fluid chambers 15 of both middle cylinders 13.
It may be clear that upon increasing the rotation frequency of the crankshafts 6a-6d, whereas the pistons 7 only displace the fluid in and out of the fluid chambers 14, 15 the reciprocating inertial forces of the piston 7 on the crankshafts 6a-6d become relatively high, because the counter force of the fluid in the fluid chambers 14, 15 is negligible. Therefore, at a certain rotation speed of the crankshafts 6a-6d the valves 16 are closed whereas both inner pistons 7 are still running in counter phase with respect to both outer pistons 7. Because of the opposite forces of the pistons 7 on the housing via the fluid in the fluid chambers 14, 15, the housing of the dynamic part 3 does not start vibrating or vibrating significantly. Increasing inertia forces of the pistons 7 on the crankshafts 6a-6d, hence on the static part 2, due to further increasing the speed of the pistons 7 can be compensated by increasing the pressure of the fluid in the fluid chambers 14, 15. In this way the speed of the crankshafts 6a-6d can be set to a desired operational speed whereas the vibration of the housing of the dynamic part 3 remains negligible, and the inertia forces of the pistons 7 on the static part are minimized. If vibration of the housing must be started, the first and/or second transmission 19, 20 are controlled such that the movement of the pistons 7 are synchronized in the same direction of movement. When closing the valves 16 during starting-up the mechanism it is preferred to close them slowly in order to balance the fluid in the fluid chambers 14, 15 and to avoid that the fluid caught in the upper fluid chamber 14 differs from that in the lower fluid chamber 15.
When a pile driver has driven a pile into the ground, for example, and the vibration of the dynamic part 3 should be stopped, the first and/or second transmission 19, 20 can be controlled such that the movement of the inner pistons 7 is opposite to the movement of the outer pistons 7, whereas the crankshafts 6a-6d remain running at the operational frequency.
In the embodiment as shown in Fig. 3 the crosshead guide 10 is disposed in the dynamic part 3. The advantage of this configuration is that it improves the flexibility of mutual displacement of the static part 2 with respect to the dynamic part 3.
From the foregoing, it will be clear that the invention provides a relatively simple but robust vibratory mechanism.
The invention is not limited to the embodiments shown in the figures, which can be varied in several ways within the scope of the invention. It is for example possible that the piston is resiliently coupled to the housing of the dynamic part through a mechanical spring instead of a fluid spring. The crankshaft may be replaced by an alternative shaft including an eccentric to which the connecting rod can be pivotally mounted. Furthermore, the mechanism is not only suitable for pile drivers, but it can be applied in alternative devices, for example for inserting elements into the ground by vibration, for compacting soils, cement, concrete, asphalt or the like.

Claims

A vibratory mechanism (1) for a pile driver comprising a static part (2) and a dynamic part (3) being movable with respect to the static part (2), characterized in that the static part (2) is provided with a drivable crankshaft (6) and the dynamic part (3) comprises a housing (13) and a vibration member (7) being drivably coupled to the crankshaft (6) through a connecting rod (8) and linearly movable with respect to the housing (13) in a direction of vibration, wherein said housing (13) is resiliently coupled to the vibration member (7).
A vibratory mechanism (1) according to claim 1, wherein the housing (13) is resiliently coupled to the vibration member (7) via a fluid spring (14, 15).
A vibratory mechanism (1) according to claim 2, wherein the vibration member is a piston (7) and the housing comprises a cylinder (13) within which the piston (7) is slidable, and the fluid spring is formed by a fluid chamber (14, 15) being present between the piston (7) and the cylinder (13).
A vibratory mechanism (1) according to claim 3, wherein the fluid spring is formed by two fluid chambers (14, 15) located at opposite sides of the piston (7).
A vibratory mechanism (1) according to claim 4, wherein the fluid chambers (14, 15) can communicate with each other through a controllable valve (16).
A vibratory mechanism (1) according to one of the preceding claims, wherein the mechanism (1) comprises at least two vibration members (7), and wherein the mechanism (1) is adapted such that under operating conditions the vibration members (7) can be driven in opposite directions.
A vibratory mechanism (1) according to claim 6, wherein the characteristics of the resiliency between the housing (13) and the vibration members (7) can be varied.
A vibratory mechanism (1) according to one of the claims 2-5, wherein the fluid spring (14, 15) can communicate with compressing means for increasing or decreasing the pressure of the fluid in the fluid spring (14, 15).
A vibratory mechanism (1) according to one of the preceding claims, wherein the mechanism (1) comprises adjusting means for adjusting the stroke of the vibration member (7) with respect to the eccentricity of the crankshaft (6).
A vibratory mechanism (1) according to one of the preceding claims, wherein the housing (13) of the dynamic part (3) and the static part (2) are connected to each other via a spring and/or a damper (18).
A vibratory mechanism (1) according to one of the preceding claims, wherein a first part (9) of the connecting rod (8) is guided by a crosshead guide (10) in the static part (2) or in the dynamic part (3) and a second part (11) thereof being fixed to the vibration member (7) is movable along its longitudinal centre line only.
A vibratory mechanism (1) according to one of the preceding claims, wherein the vibration speed of the vibration member (7), the weight of the housing (13) and the characteristics of the resiliency between the housing (13) and the vibration member (7) are selected such that the vibration member (7) and the housing (13) substantially vibrate in counter phase under operating conditions, and wherein the weight of the vibration member (7) is selected such that its inertia force of the first order substantially balances the inertia force of the housing (13).
A pile driver comprising a vibratory mechanism (1) according to one of the preceding claims.
A pile driver according to claim 13, wherein the static part (2) is provided with driving means (12) for driving the crankshaft (6).
A pile driver according to claim 14, wherein the driving means is an internal combustion engine (12).